[libvirt] [PATCH 1/3] Revert "storage: For FS pool check for properly formatted target volume"

[Peter Krempa]

On Thu, Jan 12, 2017 at 19:45:52 -0500, John Ferlan wrote:
> 
> 
> On 01/12/2017 09:41 AM, Peter Krempa wrote:
> > On Thu, Jan 12, 2017 at 09:36:01 -0500, John Ferlan wrote:
> >>
> >>
> >> On 01/12/2017 09:24 AM, Peter Krempa wrote:
> >>> The check does not work properly (crashes) with netfs filesystems and
> >>> also checking that a device is not empty when attempting to mount a
> >>> filesystem is not very usefull since the mount will fail anyways.
> >>>
> >>> As the code would improve only a very minor corner case I don't really
> >>> see a reason to have this code at all.
> >>>
> >>> This code would also fail if libvirt is compiled without support for
> >>> blkid and without parted.
> >>>
> >>> This reverts commit a11fd69735e6951cda9bf256d8e423696a441aa4.
> >>> ---
> >>>  src/storage/storage_backend_fs.c | 13 ++-----------
> >>>  1 file changed, 2 insertions(+), 11 deletions(-)
> >>>
> >>
> >> Instead of reverting why not just fix the issue.
> > 
> > Because I think the whole check is pointless. It's valid only when
> > mounting a local filesystem, and in that case basically the same check
> > is done when mounting the filesystem by the kernel.
> > 
> 
> Here's the difference between the check and removing the check (not
> withstanding the no PARTED and no BLKID available)...
> 
> Create a pool using ext4, start it - life is happy.  Destroy the pool.
> Define a pool using xfs.  Start it
> 
> w/ my change:
> 
> # virsh pool-start fs
> error: Failed to start pool fs
> error: Storage pool already built: Device '/dev/sde' formatted cannot
> overwrite using 'xfs', requires build --overwrite

I think that the error code and the message are in fact misleading here.

You are starting the pool not building it, so both the message comming
from the error code and the free form string state nonsensical facts.

> 
> w/o my change (e.g. if the change is reverted):
> 
> # virsh pool-start fs
> error: Failed to start pool fs
> error: internal error: Child process (/usr/bin/mount -t xfs /dev/sde
> /home/vm-images/fs) unexpected exit status 32: mount: wrong fs type, bad
> option, bad superblock on /dev/sde,
>        missing codepage or helper program, or other error
> 
>        In some cases useful info is found in syslog - try
>        dmesg | tail or so.
> 

While this is a bit too verbose, but in my opinion describes the problem
better.

Peter
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